Measurement device and method for analyzing a sample gas by infrared absorption spectroscopy

A measurement device for analyzing a sample gas by infrared absorption spectroscopy, comprising:

• an ante-chamber configured to homogenize the sample gas to be analyzed,
• a measurement chamber arranged to receive homogenized sample gas from the ante-chamber,
• a laser being arranged in relation to the measurement chamber such that light being emitted from the laser radiates through the measurement chamber, wherein the light being emitted from the laser has a frequency in a range of from 2.498*107 MHz to 1.499*108 MHz,
• a detection device detecting the light being emitted from the laser and radiated through the measurement chamber, and
• an evaluation unit evaluating signals generated by the detection device regarding a light absorption occurred in the measurement chamber, wherein
• the ante-chamber has a single inlet through which the sample gas enters the ante-chamber and at least two branchings of different length and diameter through which parts of the sample gas pass through, wherein the sample gas from the single inlet is separated into the parts of the sample gas by the at least two branchings and the parts of the sample gas are brought together again after the at least two branchings, a total cross section of the at least two branchings being equal to or greater than a cross-section of a single tube that delivers the homogenized sample gas from the ante-chamber to the measurement chamber, wherein
• the laser is a narrowband emitting laser having a line width of less than 0.2 cm−1 and being smaller than or equal to a width of an infrared absorption line to be measured of the homogenized sample gas, wherein
• the laser is designed and arranged such that the laser frequency is varied periodically within a defined spectral range having a width of between 0.5 cm−1 and 60 cm−1, wherein the laser frequency and its variation are chosen such that at least two infrared absorption lines to be measured of the homogenized sample gas lie in the defined spectral range, wherein
• the evaluation unit is designed and arranged to determine a ratio of two isotopes of the homogenized sample gas on the basis of the light absorptions occurring at two absorption lines, wherein
• the detection device is designed and arranged such that it detects the light being emitted from the laser and radiated through the measurement chamber in such a time-resolved manner that the light absorption can be determined frequency-resolved within the defined spectral range, wherein
• the detection device carries out a single absorption measurement within 10−5 s or faster, wherein
• the measurement device is suited and can be arranged to measure the respiratory gas of a human or animal as sample gas, wherein
• the measurement chamber has an open construction devoid of obstructions which could hinder the flow of the homogenized sample gas, wherein the measurement device has a constant cross section for the sample gas flowing through so that a laminar flow of sample gas is established in the measurement device, wherein
• the respiratory gas exchanges in the measurement chamber only by the respiration of the human or animal, and wherein
• the respiratory resistance of the measurement device is less than 60 mbar.